1. Technical Field
The present invention relates to a method of operating a transmitter to multicast data blocks over a network.
2. Description of Related Art
In network terminology, sending a data block (i.e. a message, packet, frame or the like) across a network to a single recipient is known as unicasting. Sending a data block to all receivers connected to a network is known as broadcasting. Sending a data block to a set of recipients that form a subset of all receivers connected to a network is referred to as multicasting. Such a set of recipients is known as a multicast group.
In broadcast networks (e.g. nearly all Local Area Networks), all receivers receive any data block placed the network. Each receiver has a network interface card that identifies frames that are intended for that receiver. In order to identify which multicast data blocks are intended for that receiver, the network interface card must store an indication of each multicast address for which the receiver is a recipient.
In networks comprising switching nodes interconnected by point-to-point links, each switching node must store, for each multicast group, an indication of which of the links connected to it lead toward members of the multicast group.
In both types of networks therefore, the amount of memory required in network components increases with the number of multicast addresses in use.
Conventional use of multicast networks often results in the use of more multicast addresses than is necessary. Furthermore, the amount of traffic generated in passing one or more multicast messages across the network is often unnecessarily high.
European Patent Application EP 0 854 604 A1 discloses a fast packet switching network that provides interconnection for peer networks that support group addressing.
Although the use of multicasting is currently at a level where the above problems do not impact heavily on network performance, a rapid rise in the use of multicast is likely to take place over the next few years. This means that there is a need to provide a more efficient way of using networks that provide a multicast capability.